Which of the following is excreted in human urine ?

Options

A. Ammonia
B. Urea
C. uric acid
D. amino acid

Answer

To determine which of the following substances is excreted in human urine, we can analyze the options provided: ammonia, urea, uric acid, and amino acids.

### Step-by-Step Solution:

1. **Understanding Urine Composition**:
- Human urine is primarily composed of water, but it also contains various waste products that are the result of metabolic processes in the body.

2. **Identifying Nitrogenous Wastes**:
- The body produces several nitrogenous wastes during metabolism, which need to be excreted to maintain homeostasis. The main nitrogenous wastes include ammonia, urea, uric acid, and creatinine.

3. **Metabolism of Nitrogenous Compounds**:
- Ammonia is a toxic byproduct of protein metabolism. Due to its toxicity, it is converted into urea in the liver, which is less harmful and more soluble in water.

4. **Ureotelic Nature of Humans**:
- Humans are classified as ureotelic organisms, meaning they primarily excrete urea as the main nitrogenous waste product. This is done to safely eliminate excess nitrogen from the body.

5. **Other Nitrogenous Wastes**:
- Uric acid is also excreted, but in smaller amounts compared to urea. It is a product of purine metabolism. Amino acids, on the other hand, are generally not excreted in urine; they are usually reabsorbed by the kidneys or utilized by the body.

6. **Conclusion**:
- Based on the information above, the primary substance excreted in human urine is **urea**. Therefore, the correct answer to the question is **option B: urea**.